The claustrum consists of the core and shell subregions. To investigate the involvement of GABAergic neurons in the circuitry in each subregion, we examined the distribution, neurochemical marker expression, and dendritic and axonal arborizations of claustral GABAergic neurons. Fluorescence in situ hybridization combined with immunofluorescence labeling revealed that approximately 10% of neuronal marker-positive cells expressed 67kDa-glutamic acid decarboxylase mRNA across the claustral subregions. Approximately 20%, 30%, and 10% of GABAergic neurons showed the immunoreactivity for parvalbumin (PV), somatostatin (SOM), and vasoactive intestinal polypeptide (VIP), respectively, in each subregion. We then injected adeno-associated virus vectors into the claustrum of PV- or SOM-Cre knock-in mice, prepared 1-mm-thick brain slices, and enhanced the fluorescent signal using the Fluorochromized Tyramide-Glucose Oxidase (FT-GO) method, a technique we have previously developed (Yamauchi et al., 2022). Following optical clearing of the slices using the ScaleS method (Hama et al., 2015), 3D image stacks were obtained with a confocal laser scanning microscope, and the dendrites and axons were reconstructed. Single neuronal reconstruction revealed that the dendrites and axons of PV and SOM neurons were preferentially localized to their respective subregions where their cell bodies were found. We also showed the axons were preferentially extended in a rostrocaudal direction, whereas the dendrites were relatively isotropic. The preferential localization could play a role in facilitating independent information processing within the local circuits of the core and shell regions.